The Sinclair Shoulder Bump Gauge Insert #20A is a precision reloading tool designed specifically for .338 Lapua cartridges with a 20-degree shoulder angle.Sinclair Shoulder Bump Gauge Insert #20ADesigned for .338 Lapua cartridge cases20-degree shoulder angle specificationPrecision machined for accurate measurementsCompatible with Sinclair bump gauge systemsEssential for precision reloaders who need to measure and control cartridge case shoulder setback for consistent chambering and improved accuracy in .338 Lapua firearms.